Prior to the present invention, various exhaust manifolds and methods of controlling exhaust gases have been disclosed in the prior art. U.S. Pat. No. 2,230,666 which issued on Feb. 4, 1941 and is entitled “Exhaust Gas Collector” discloses a plurality of laterally spaced exhaust pipes fluidly connected to the cylinders of an associated internal combustion engine open to a diverging funnel-like main exhaust tube providing reduced back pressure and thereby increasing the power of the engine. U.S. Pat. No. 4,288,988 which issued on Sep. 15, 1981 and is entitled “Method and Apparatus for Improving the Gas Flow in an Internal Combustion Engine Exhaust Manifold” discloses a method and apparatus for damping pressure oscillations in the exhaust manifold of an associated engine by throttling the exhaust gas near the outlet of the cylinders and then accelerating the gas flow in the manifold by providing a uniform flow section therein which is substantially smaller than the cylinder bore. U.S. Pat. No. 5,860,278 which issued on Jan. 19, 1999 and is entitled “Apparatus and Method for Providing a Compact Low Pressure Drop Exhaust Manifold” discloses a method and apparatus for improving flow through the manifold and decreasing pressure drop to enhance engine performance.
While these and other prior manifold constructions control flow of engine exhaust gas as disclosed, one drawback is that such constructions can result in exhaust interference (i.e. a portion of the engine exhaust gas reflected back up the exhaust tube toward non-firing upstream engine cylinders) and reduced output depending on the exhaust order of the engine cylinders. It is therefore desirable to provide an exhaust manifold that is capable of reducing undesirable pneumatic interaction between cylinders and optimizing exhaust flow.
It is known in the art that one solution for reducing undesirable pneumatic interaction is to provide an exhaust gas intake branch on the manifold adjacent to each cylinder of sufficient length (i.e. greater than eight inches) to permit the engine to fire the upstream cylinders prior to exhaust gas from downstream cylinders reaching the main exhaust tube. In this solution, exhaust gas entering the main exhaust passage of the manifold from upstream cylinders creates a sufficient downstream pressure on the exhaust gas previously emitted from downstream cylinders to prevent undesirable pneumatic interaction. However, the compact size of modern vehicle engine compartments makes such designs difficult due to their bulky configurations. It is therefore desirable to provide an exhaust manifold that requires a minimal amount of space within the engine compartment while reducing undesirable pneumatic interaction between cylinders.